Conventionally, a method of joining heating elements and heat sinks with a heat conductive sheet is known as a method for cooling heating elements such as semiconductor elements installed in electronic devices. For example, Japanese Unexamined Patent Application Publication No. 2001-310984 discloses a heat conductive molded body molded from a heat conductive elastomer composition containing specific amounts of thermoplastic elastomer, magnesium oxide, and soft magnetic material powder, and proposes providing this molded body between parts to be cooled and a heat sink.
Furthermore, Japanese Unexamined Patent Application Publication No. 2003-238760 discloses “a non-halogen flame retardant heat dispersing sheet, comprising 100 to 150 weight parts of a metal hydroxide based flame retardant, 1 to 10 weight parts of red phosphorus, and 500 to 700 weight parts of heat conductive powder in 100 weight parts of binder resin comprising 60 to 90 weight % of ethylene acrylate polymer and 10 to 40 weight % of ethylene-methyl acrylate copolymer” as a heat dissipating sheet with excellent flame retardancy.
However, in recent years, the heat generating density of heating element surroundings have further increased because of higher integration and reduced size of electronic devices, and the thermal properties required of conventional heat conductive sheets do not necessarily provide sufficient effects. In particular, issues that were not required of conventional heat conductive sheets include long term stability when used at the high temperatures generated in recent electronic devices.